In various kinds of pad printing and press printing operations determining the dilutability or viscosity of the relevant preparation is a crucial factor in achieving high print quality. Generally before the printing operation commences a value that may be referred to as a viscosity reference value is set or determined as the value at which the ink viscosity should be maintained. It is common for the viscosity of the preparation to change considerably during the printing application, and thus a diluting agent must be added to the preparation for maintaining the desired viscosity. This occurs in pad ink printing where it is known that the surface viscosity of the preparation is susceptible to abrupt changes.
Manual methods of maintaining the desired viscosity include mixing the diluting agent into the preparation and then taking measurements at given time periods to determine the viscosity. If the viscosity exceeded the desired reference value measured amounts of the diluting agent would be manually added in order to achieve the reference value in a trial and error method. In addition, graphical and mathematical tables and registers can be prepared that are specific for each preparation and diluting agent system. However, these methods are laborious and prone to methodological errors.
The Kellner Patent (German Patent 3,602,309) discloses an apparatus for determining the dilutability of viscous preparations that are particularly used in intaglio and flexographic printing inks. The Kellner Patent includes a flowmeter with a diluting agent counter mounted on the diluting agent tube. A reference value sensor, a start button, a timer and a sensor having a rotator immersed in a sample vessel are linked so that after the timer is activated and a preset interval elapses, a valve opens and the diluting agent's flow rate is displayed. As soon as the actual value of the viscosity attains the reference value, the valve closes and the counter for the diluting agent can be returned to the zero position. It should be noted that in the Kellner Patent the addition of the diluting agent doesn't occur until the appropriate thixotropic reduction of the preparation is achieved.